Positron emission tomography (PET) is a specialized radiology procedure that generates three-dimensional images of functional processes in a target organ or tissue of a body. Specifically, in PET studies, a biologically active molecule carrying a radioactive tracer is first introduced into a subject's body. The PET system then detects pairs of gamma rays emitted indirectly by the tracer and reconstructs a three-dimensional image of the tracer concentration within the body by analyzing the detected signals. Because the biologically active molecules used in PET studies are natural substrates of metabolism at the target organ or tissue, PET can evaluate the physiology (functionality) of the target organ or tissue, as well as its biochemical properties. Changes in these properties of the target organ or tissue may provide information for the identification of the onset or progression of a disease before an anatomical change relating to the disease become detectable by other diagnostic tests, such as computed tomography (CT) or magnetic resonance imaging (MRI).
Furthermore, the high sensitivity of PET—in the picomolar range—may allow the detection of small amounts of radio-labeled markers in vivo. PET may be used in conjunction with other diagnostic tests to achieve simultaneous acquisition of both structural and functional information of the body of a subject. Examples include a PET/CT hybrid system, a PET/MR hybrid system.
A PET/CT image may be obtained using a PET/CT hybrid system. During a scan in the PET/CT system, a subject may undergo respiratory motion, which may cause artifact in an image. The PET data may be corrected based on the CT data in order to compensate for the attenuation of the PET projection data caused by loss of detection of true coincidence events. A PET image may be obtained based on the corrected PET data. To this end, the CT data and the PET data may need to be matched with respect to the scanning of a same area of a subject; a mismatch may subsequently cause artifacts in the PET image, which in turn may affect an interpretation of the PET image, or diagnose on the basis of the PET image. During a scanning of the subject by the PET/CT hybrid system, if the scanning is operated for chest or upper abdomen examinations, respiratory motion of the lungs and/or cardiac motion of the heart of the subject may lead to the mismatch. Thus, it is desirable to develop a method and system for matching such acquired CT data and PET data to reduce the effect of respiratory and/or cardiac motion of the subject and improve the quality of a PET image reconstructed accordingly.